Resolution of imaging systems is ultimately controlled by the physical pupil or aperture size. Unfortunately, large monolithic pupil sizes are often incompatible with a number of engineering and manufacturing constraints.
An alternative to a monolithic pupil imaging system is a multi-pupil imaging system. Two such systems are the segmented pupil imaging system and the multiple pupil imaging system. The segmented pupil system has effectively one large pupil created by making individual segments of the pupil and placing them together. The individual segments are oriented by tip and tilt and piston adjustments to form one smooth optical aperture such that light from an object passing through each of the segments comes together as a single image on a single focal plane. These inter-pupil adjustments assure that an image is formed on the focal plane as it would be with a single non-segmented pupil.
In the multiple pupil system, several separated imaging systems are used. A series of optical elements is used to combine the images onto a common focal plane. As with the segmented pupil, tip and tilt and piston adjustments assure that the images of an object formed by each aperture add coherently as a single image on the focal plane.
In both of these multi-pupil systems, the tip and tilt adjustments increase the intensity of the image by overlapping the images from each pupil. However, resolution of the system is not optimized. The resolution of an imaging system is a measure of its ability to reproduce high spatial frequencies in an image which are present in the scene being imaged. In multi-pupil imaging systems, resolution is a function of inter-pupil piston displacements or phase adjustments. As the inter-pupil phase difference is reduced, the resolution of the multi-pupil imaging system improves.